Coating, printing, and related processes conventionally are carried out by dissolving film-forming ingredients in a volatile solvent, applying the resulting composition to a substrate, and drying and curing the transferred material with or without heating, whereby the volatile solvent is released to the atmosphere. Evolution of the solvent tends to lengthen the hardening process and to leave voids and pinholes in the cured coatings, making them porous. Emission of volatile solvents tends to pollute the adjacent air unless costly arrangements are made to recover practically all of the solvent, and release of flammable volatile solvents may create fire and explosion hazards. Heating often is required to hasten removal of the solvent, but the higher temperatures produced may damage the substrate, or may cause running and deformation of the coating while it still is soft.
Solvent-free mixtures of epoxide materials may be prepared based essentially, for example, on certain epoxidic prepolymers such as the reaction products of epichlorohydrin with bisphenol A or with novolaks. Such prepolymers have been blended with various monoglycidyl ethers, or with a glycol diglycidyl ether, primarily to modify the viscosity of the prepolymer. Such mixtures can be shaped, as by coating, and then treated with an activated cationic initiator to cure the resin. However, these prepolymeric mixtures do not provide the rheological properties most desirable for certain coating or related operations, or are unsuited for application to various types of substrates. Coating and printing machines require unique combinations of properties to permit smooth and rapid flow of the coating and printing compositions through the machines for proper application to the substrate web or sheets supplied to the machines. It also has been observed that modification of the solvent-free epoxide materials with socalled reactive diluents, such as monoglycidyl ethers, to obtain the desired rheological properties tends to decrease the speed of curing and to diminish the hardness of the material after initiation of polymerization and curing, giving a more or less soft or tacky finish rather than a tough, solid finish. Efforts to avoid this problem by the inclusion of hardeners, such as amines, amides, or anhydrides, lead to premature curing immediately upon mixing and a tendency to brittleness in the cured material. It is an object of the present invention to provide epoxide blends suitable for use in polymerizable compositions, and to provide a related polymerizing process, which substantially avoid these difficulties and disadvantages encountered with prior materials and processes.